1. Field of the Invention
The present invention relates to data recording and playback, and more particularly relates to the recording of digital data onto a recording medium such that said medium is suitable for playback on video playback apparatus adapted for different video signal formats.
2. Background Art
The development over the past several years of the optical disc has led to the recent commercialization of the video optical disc. The video optical disc is a disc approximately the size of an LP phonograph record which, instead of the grooves of a phonograph record, has recorded thereon spiral tracks of optically readable indicia. The disc is read by imaging a beam of laser light to a tiny spot on a track, rotating the disc so as to effect scanning of the spot along the track, and recording the laser light which emerges from the disc modulated by the pattern of the indicia along the track. Video optical discs have relately large storage capacity and, for example, can provide over two hours of video playtime per disc.
The large storage capacity of the optical disc has led to the development of other applications besides the recording of video program information for later playback. For example, the optical disc is being developed as a data storage medium for digital computers.
Another desired application is the recording of digitized audio information for later playback. It is known, for it example, that very high fidelity audio recording can be effected by using pulse code modulation ("PCM") techniques. PCM encoding and recording techniques have been used in connection with conventional phonograph records to preserve fidelity and signal to noise ratio in the signal processing between performance and the recording on the record.
The optical disc may be used to record such PCM encoded audio directly, due to the high information storage capability of the disc.
It is desired to record such PCM encoded audio data onto an optical disc such that the disc can be played on a conventional video disc player apparatus with minimum necessary modification for such digitized audio playback. This would permit the utilization of existing video optical disc player apparatus technology to a large extent to permit, for example, the use of a single apparatus for video optical disc and audio optical disc playback.
A problem posed in achieving such a result is that video optical discs and their associated players are typically standardized to the local commercial television formats, and such formats are not uniform throughout the world. For example, in the United States, under the NTSC format, horizontal intervals are provided at a frequency of approximately 15 kilohertz, and 525 lines are provided in each frame of video information. In Europe, under the PAL format, the horizontal interval frequency is approximately the same; however, 625 horizontal lines are provided for each frame of video.
Consequently, video discs and their associated video disc player apparatus are different in United States and Europe, each being designed for compatibility with commercial television sets for the respective formats. It is desired to provide encoded audio optical discs compatible for playback on video optical disc players of either format. This would permit a commercial standardization of such discs similar to that which exists in the phonograph industry.
However, due to the differences in formats, such a standardization has heretofore been impossible. Video optical disc player apparatus have internal circuits associated with the maintenance of precise disc rotation speed which circuits are directly tied to the horizontal and vertical sync pulses recovered from the video disc. These circuits depend upon the ratio of the vertical sync pulses to horizontal sync pulses for their function. When, for example, a video disc formatted for broadcast format is played on a player apparatus designed for another broadcasting format, the imcompatible ratio of vertical sync pulses to horizontal sync pulses results in disruption of the internal circuitry of the apparatus and unsynchronized signal recovery.
The present invention overcomes these problems and provides a method and apparatus for the recording and playback of encoded audio information such that optical discs provided with such encoded audio data in this format may be played on video optical disc player apparatus of either of at least two different video broadcasting formats while providing smooth and uninterupted playback of the audio.